Source Citation

Abstract

Objective

To develop a prognostic system for patients with carotid transient ischemia or minor
stroke.

Design

An inception cohort was assembled between 48 hours and 30 days after a first carotid
transient ischemic attack or minor stroke and was followed for 2 years.

Setting

An urban teaching hospital.

Patients

Of 352 patients who had carotid ultrasonography between 1984 and 1987, 142 patients
met the definition for transient ischemic attack or minor stroke and completed the
study. Patients with artificial heart valves were excluded.

Assessment of prognostic factors

Data regarding 15 potential predictors of death or stroke were collected from medical
records.

Main outcome measures

Stroke or death within 2 years.

Main results

38 patients (27%) had a stroke or died within 2 years. 3 factors were predictive of
stroke or death: age > 65 years (relative risk [RR] 2.55, 95% CI 1.23 to 5.25),
diabetes mellitus (RR 2.78, CI 1.47 to 5.27), and severe hypertension (RR 1.92, CI
0.95 to 3.87). Points were assigned to the 3 predictors by rounding the estimated
RR from a proportional hazards analysis to the nearest integer, and a total point
score was calculated for each patient by summing points from the individual predictors.
40 patients in risk group 1 (0 points) had a rate of stroke or death of 2%; 80 patients
in group 2 (1 to 5 points) had an event rate of 31%; and 22 patients in group 3 (6
to 8 points) had an event rate of 54% (P < 0.001). In an independent test sample, the corresponding event rates were 12%,
21%, and 31% (P = 0.04), respectively. 2 additional predictors were subsequently added to improve
the performance of the system: coronary heart disease (1 point) and the distinction
between transient ischemia and stroke for the baseline event (2 points). The final
risk groups 1 (0 to 2 points), 2 (3 to 6 points), and 3 (7 to 11 points) had event
rates of 3%, 27%, and 48% (P < 0.001) in the original cohort, and 10%, 21%, and 59% (P < 0.001) in the test cohort.

Conclusion

For patients with carotid transient ischemia or minor stroke, the combination of 5
clinical features (age > 65 years, diabetes, hypertension, coronary heart disease,
and stroke [rather than transient ischemic attack] as the baseline event) predicted
the risk for subsequent stroke or death.

Source of funding: Dr. Kernan was a Robert Wood Johnson Clinical Scholar.

Commentary

In this cohort study of patients with anterior-circulation transient ischemic attacks
or minor strokes, the authors found that the risk for recurrent stroke or death is
increased in persons with advanced age, hypertension, diabetes mellitus, or comorbid
cardiac disease. These findings are consistent with those of other cohort studies.

A prognostic index always does less well in predicting outcomes in a different set
of patients than in the group used to generate the index (1), as was the case in this study. The modified index performed better when applied
to the test cohort but not when applied to the original cohort. The wide 95% confidence
interval for the high-risk group in the test cohort should also be noted.

This study does not attempt to address the issue of possible therapeutic thresholds.
It should not be assumed that low-risk patients as defined by this index do not need
prophylactic therapy to prevent future events. For example, a 64-year-old man with
atrial fibrillation and a minor stroke would be in the low-risk group but should receive
anticoagulation therapy to prevent future events (2). The clinical value of this study is that it clearly defines risk factors for subsequent
events and shows that patients with multiple risk factors are at greater risk than
those with few or no risk factors. Like all models, this one needs to be used with
reasoned clinical judgment.

James Kitchens, MDToronto General HospitalToronto, Ontario, Canada

References

2. The Boston Area Anticoagulation Trial for Atrial Fibrillation Investigators. The effect of low-dose warfarin on the risk of stroke in patients with nonrheumatic
atrial fibrillation. N Engl J Med. 1990;323:1505-11.